Society's increasing concern with the environmentally safe disposal of industrial wastes has led to the development of a variety of processes in which such wastes are used to form, or are incorporated in a cementitious material. Upon hardening, such material (when properly formulated) is suitable for disposal or for use as a construction or landfill material.
The adaptability of such processes for the disposal of a wide variety of waste materials, including organic waste materials, is suggested, for example, in British Patent No. 1,485,625 to Chappell and U.S. Pat. Nos. 3,947,284 to Kitsugi et al., 3,980,558 to Thompson, and 4,209,335 to Katayama et al. The teachings of these references are directed primarily to the utilization of Portland cement as the encapsulation material. Portland cement has been widely applied for the solidification or stabilization of wastes to meet RCRA (Resource conservation and Recovery Act) and CERCLA (Comprehensive Environmental Response, Compensation, and Liability Act) requirements.
Portland cement produces calcium silicate hydrates as its principal reaction product. This cement has been utilized in the prior art for its cementitious reactions either alone or in conjunction with other cementitious material. In particular, Portland cement has been utilized in the prior art in combination with fly ash to stabilize oily wastes. These combinations, however, which typically require on the order of 60% cement and 40% fly ash, must be used at a dosage rate of at least 25 weight percent based upon the wet weight of the oily waste to be stabilized. From an economic viewpoint, it is highly desirable to replace the cement in these prior art compositions with other less expensive reagents.
In addition to Portland cement, pozzolanic cement has also been utilized, eight by itself or in conjunction with filler material, such as aggregate, for various purposes wherein structural integrity, landfill or support is desired. Initially, the term, "pozzolanic" referred to a type of volcanic ash which by itself is not cementitious, but, when combined with lime or a lime generating material and water, hardens over time. Pozzolans generally are known to react slowly with alkaline earth oxides and moisture, ultimately setting up into a hard rock-like material.
Fly ash is a finely divided particulate material collected from combustion stack gases, typically from the combustion of pulverized coal in boilers. Fly ash may be considered an "artificial pozzolan," as distinguished from "natural pozzolans," which are generally of volcanic origin. Typically, a mixture of lime, fly ash and water produces calcium silicate hydrates and the reaction system can incorporate some organic compounds. These mixtures, although useful in stabilizing organic compounds, are not as effective as reagent mixtures containing Portland cement. Thus, the prior art more commonly uses Portland cement but may also suggest the use of byproduct materials such as fly ash or kiln dust (such as the waste by-product from lime or cement kilns), alone or in combination with Portland cement, to stabilize waste material including some organic wastes.
Examples of prior art references which teach the use of byproduct materials to produce solid bodies and/or to stabilize wastes include U.S. Pat. Nos. Re. 29,783 to Smith et al. (lime and fly ash to stabilize sulfate-containing waste such as acid mine drainage sludge), 4,226,630 to Styron (Powder River Basis fly ash to form solid, leach resistant bodies when combined with aqueous heavy metal sludges which can contain other inorganic ions); 4,397,801, 4,344,796, and 4,250,134 to Minnick (Cementitious compositions comprising fluidized bed combustion ash and/or fly ash which harden when mixed with water).
When using prior art fly ash and/or kiln dust compositions without Portland cement, however, the reagent compositions must typically be used in large quantities (relative to the amount of waste being stabilized) in order to cementitiously react to form a hard body. Moreover, when using prior art combustion byproduct reagents such as fly and bed ashes to stabilize organic wastes these reagents alone are not very reactive and thus are not very effective (in the absence of Portland cement) in encapsulating low solids/high moisture content wastes.